Somehow I skipped or forgot this about SQL UPDATE command.
When I do UPDATE on a database row, does UPDATE check for the same values and updates only not-same ones or it simply overwrites all cells in the row?
Note: under UPDATE I mean updating all columns
It will Overwrite the data.
Of course it will overwrite the field, but it doesn't really matter, it's the same value.
Related
Hello I have a simple mapping, that basically has a router to decided whether the record has to be inserted or updated and then use Update Strategy to flag the row.
The records were updating and inserting as expected, I had to make some modifications to the logic and did the required changes.
And now the records are no more getting flagged as an insert or an update. Below settings :
1) DD_UPDATE and DD_INSERT coded in the update strategy.
2) At session level, treat source as set to Data Driven.
3) The 2 targets set to update as update and insert respectively.
I even ran a debugger to see what is happening, the insert update records are passing through the update strategy, however the row type is set to blank when its passed to the target instance :( what could be the issue?
I finally found the issue. Both the Update Strategy's were corrupted. deleting and recreating the update strategy's resolved the issue :) Thanks for your help!
Is there an approach for updating all items in an attribute(column) ?.
I'm updating the values one by one using a for loop, but it takes a while. I can easily update a whole row in my table by benefiting from DynamoDB mapper, but cannot find a similar functionality for an attribute.
No, the only way is to do a scan over the hash space and update each item.
Is there a way of disabling the item in the database instead of deleting it.
Any one with any idea , Do reply
i guess it depends on what you mean by 'disabling'. you could add a BooleanField called e.g. disabled, and then filter your queries (probably best done via a custom manager) so instead of
Mymodel.objects.all()
do
Mymodel.objects.filter(disabled=False).all()
Not in SQL. What you probably would be ending up doing to solve the problem is either
Moving the "disabled" values to another table, either by a trigger or stored procedure
or
Adding an 'active' flag to the table with default value 1 and setting it to 0 instead of deleting. That would require an extra condition on every query (and active=1) that does not want to query disabled records.
You can set a field in the table which you set if the row is valid or unset if the row is deactivated.
I have two threads, one which runs something like update t set ColA=foo and the other runs update t set ColB=foo. If they were doing raw SQL statements there would be no contention, but since Django gets and saves the entire row, a race condition can occur.
Is there any way to tell Django that I just want to save a certain column?
Update old topic.
Now, we have update_fields argument with save:
If save() is passed a list of field names in keyword argument
update_fields, only the fields named in that list will be updated.
https://docs.djangoproject.com/en/stable/ref/models/instances/#specifying-which-fields-to-save
product.name = 'Name changed again'
product.save(update_fields=['name'])
You are correct that save will update the entire row but Django has an update which does exactly what you describe.
https://docs.djangoproject.com/en/stable/ref/models/querysets/#update
I think your only option to guarantee this is to write the raw SQL by hand by using Manager.raw() or a cursor depending on which one is more appropriate.
I have a field defined in my table as DATE and want it to automatically populate with the current system date when someone access the update form in my APEX application. But the date doesn't update. It was working when I first added it, but now when you pull up the update page it only shows the date that's in the table.
In Oracle, a default on a column means that if a record is inserted into the table without mentioning that field, then use the default. My guess is that since the field is displayed on your page, you are writing NULL or spaces to it, so it is definitely included in the insert statement.
So you need to either take it off the page, add an update trigger, or even better, write a process in Apex to update it whenever the record is modified -- perhaps an After-Submit computation.